chore: review FIXMEs and TODOs (#272)

This patch also adds issue IDs when appropriate:

```rust
// FIXME(#XX): the foo-bar problem
// TODO(#XX): add support for feature baz here
```

This way, it’s easier to lookup the places relevant for tackling a
specific issue of the tracker, and conversely, it’s easier to
know which problem are "properly" tracked and which are not.

crates/ironrdp-svc/src/lib.rs

@@ -170,7 +170,7 @@ pub trait StaticVirtualChannelProcessor: AsAny + fmt::Debug + Send {
 
     #[doc(hidden)]
     fn is_drdynvc(&self) -> bool {
-        // FIXME: temporary method that will be removed once drdynvc is ported to the new API
+        // FIXME(#61): temporary method that will be removed once drdynvc is ported to the new API
         false
     }
 }